Devices for infusing to a patient a beneficial agent such as a drug diffused in a medical liquid are known in the art. The most common device utilizes an elevated glass or flexible container having a beneficial agent diffused in a medical liquid which is fed by gravity to a patient's venous system via a length of flexible plastic tubing and a catheter. The rate of flow in this type of device is commonly regulated by an adjustable clamp on the tubing. This set-up suffers from the drawback of requiring a relatively stationary patient and is dependent on the height differential between the medical liquid and the patient for accurate delivery rates.
An additional type of infusion device utilizes electro-mechanical components and a pump to provide fluid propulsion of the medical liquid for infusion into the patient. Such electronically controlled infusion devices, however, suffer from several drawbacks, including the cost of such electrical components as well as the limit such electrical components and the necessary power source place on the size and thus portability of the device.
Devices in the art are also utilized which employ an elastomeric bladder which contains the medical liquid to be infused under pressure for infusion. A typical elastomeric bladder device includes housing, a plug fixed in one end of the housing which includes aperture that extends through the plug, and a tubular elastomeric bladder in the housing for receiving the liquid under pressure. One end of the bladder is sealingly attached to the plug, with the interior of the bladder communicating with the aperture of the plug. A conduit connected to the plug aperture defines with the aperture a dispensing passageway for transporting the medical liquid from the bladder to the infusion site of the patient. A flow regulator is disposed somewhere in the dispensing passageway for permitting the medical liquid to flow from the bladder to the dispensing passageway at a predetermined rate into the patient.
Another type of device utilizes a syringe-type construction having a plunger disposed within and making sliding, sealing contact with the interior surface of the syringe barrel. A biasing means such as a spring or an elastomeric band is also provided between the plunger and the housing. Medical liquid to be infused is received under pressure within the interior of the barrel in a chamber defined by the interior of the barrel and the plunger. The pressurized medical liquid forces the plunger to bias the biasing member thereby providing a source of medical liquid under pressure. The pressurized medical liquid is provided to a patient through the conduit means similar to the elastomeric bladder type device.
A particular problem in the infusion devices in the art is achieving a relatively constant flow rate for the infusion of the liquid. The relatively constant flow rate is particularly important when infusion over extended periods of time, such as 24 or 48 hours, is required for the drug therapy. In the infusion devices utilizing elastomeric bladders, such relatively constant flow rates have been achieved by means such as prestressing the elastomeric bladder and the use of costly bladder material. The use of such additional prestress housing and expensive bladder material, of course, adds to the costs of such disposable infusers. In the syringe-type infusion devices, the rate of infusion is restricted to a relatively short period of time because of the accuracy problem found in such designs.
What would thus be desirable would be a disposable infuser device which is able to give relatively constant flow rates over extended periods of infusing while maintaining a comparatively low manufacturing and materials cost factor. The present invention achieves these requirements.